The nucleation of water droplets on a substrate from ambient atmosphere poses an ongoing problem for viewing and vehicle operation under high humidity conditions. The operation of automobiles, spacecraft, and aircraft are all compromised by poor visibility associated with fog condensation on a viewing substrate of such vehicles and craft. Other transparent viewing surfaces also exhibit diminished performance as a result of droplet nucleation on such surfaces. These other surfaces include glasses, goggles, camera lenses, and binoculars. Additionally, with unmanned aerial vehicles and underwater craft proliferating, concerns about visual impairment associated with condensation on viewing substrates in such unmanned vehicle has become an increasingly urgent problem.
Traditionally, for preventing fog on various substrates, a method of coating a surface with a surfactant that has wetting property is generally used. The duration of the anti fog effect by using this method is limited and regular re-application is required. Moreover, the performance under high humidity conditions is not good because the surfactant cannot hold a large amount of water that condensed on the surface. Hence, the conventional anti-fog develops rivulets of water and has a streaked transparency.
More recently, the field has learned to appreciate that substrate fogging can be inhibited by coating a substrate with a water-absorbing material, as opposed to a surfactant that simply modifies the wetting properties of a substrate. Water absorbing materials that have been used include starch-based polymers, cellulose-based polymers, polyvinyl alcohol-based polymers, acrylic polymers, and polyether-based polymers. The use of these water absorbing polymers has extended the duration of an anti-fog effect relative to surfactant-based compositions. Water absorbing material deposition techniques for an anti-fog film include reliance on heat treatment (U.S. Pat. No. 5,976,680), vacuum processes (U.S. Pat. No. 6,287,683), and dip-, spray-, or spin-coating (U.S. Pat. No. 6,394,613). A characteristic common to these anti-fog film deposition techniques is the inclusion of two or more treatment steps to apply an anti-fog film. Additionally, these techniques require a catalyst needed to crosslink the polymer into a final film, heat treatment to temperatures of greater than 80° C., vacuum process or the necessity to remove the substrate from the substrate mounting in order to perform the dip coating, spray coating or spin coating to achieve an optically smooth anti-fog film, or combinations of these processes. As a result of these limitations associated with prior art techniques for applying a water-absorbing material containing anti-fog film onto a substrate, the ability to reapply such an anti-fog composition while a substrate is in field use is severely hampered.
Thus, there exists a need for a moisture absorbing anti-fog composition and a process for the use thereof that is readily applied in the field to a substrate through resort to the conventional trigger spray application, propellant aerosol, or a sponge or cloth for wipe application onto the substrate desired to have an anti-fog film thereon. There also exists a need for a process to apply such a composition from a kit to provide an anti-fog film on a substrate.